[3] The potential importance of the Yixian Formation was initially recognized during the time the Empire of Japan occupied China's Rehe ("Jehol") Province after the Defense of the Great Wall in 1933.

[3] When originally estimated, the Yixian Formation was believed to have been deposited over a period of about 7 million years, during the later Barremian and early Aptian stages.

However, the duration of deposition of the formation was narrowed in 2016 by analyzing continuous sedimentary cores to roughly the interval between 129.7 ± 0.5 and 125.2 ± 0.9 million years ago.

If true, this would make the entire duration of deposition of the Yixian Formation about 1.633 ± 0.078 million years, which is considerably shorter than the initial estimates and would place it wholly within the Barremian stage of the Early Cretaceous.

Various revisions to this arrangement have been made by several authors in the period from 2000 to 2010, including the consolidation of the Jiulongsong and Hengdaozi members into what is today called the Jianshangou Unit.

Some authors do not consider the Dawangzhangzi and Huanghuanshan units to be distinct enough to separate, opting instead to call this interval the "Undivided Upper Yixian Formation".

[13] Wang and colleagues made efforts to standardize the stratigraphy of the lower half of the Yixian Formation and their scheme further subdivided the Jianshangou Member into (in ascending order) the Dajianshanzi, Anjiagou, Hengdaozi, and Huangbanjigou beds.

Furthermore, the upper units of the Yixian Formation are generally less fossil-rich, and have received considerably less attention in the scientific literature, and so their stratigraphy remains somewhat unresolved.

[11][13] With the diversity of plant life in the Yixian well known, including examples of a variety of petrified wood and growth rings, and with the help of chemical analysis, scientists have been able to determine the climate of the formation.

The Yixian flora was dominated by conifers closely related to modern species that are found mainly in subtropical and temperate upland forests.

This indicates a temperate climate with unusually cold winters for the generally warm Mesozoic era, possibly due to northern China's high latitude during this time.

[3] Studies of vertebrates have shown support for the division of the Jehol into phases, and the diversity of fish in the Yixian was distinct from older and younger formations, with Lycoptera as the dominant species.

Volcanic activity, along with periodic wildfires, and noxious gasses released from the lake bottoms caused the ecosystem to be continually destroyed and regrown.

This, along with the wide diversity of habitats in the surrounding region, may have contributed to the fast diversification of life forms present in the Yixian ecosystem.